Direct contact instrument calibration system

Abstract

Systems and methods for calibrating an instrument having a tool and a work surface. An exemplary instrument may comprise a support member including a conductive surface. The instrument also may comprise a fluid-transport device including a conductive tube having an open end. A drive mechanism of the instrument may include a motor operable to drive movement of the surface and the tube relative to one another along an axis and into contact with one another. A circuit of the instrument may include a voltage source and the tube. A control module may be configured to calibrate a relationship between the drive mechanism and a position of the tube and/or surface along the axis based on a sensed change in an electrical property of the circuit that occurs when the tube and the surface contact one another.

We claim: 
     
         1 . An instrument having a calibration system, comprising:
 a support member including an electrically grounded, conductive surface;   a fluid-transport device including an electrically conductive tube having an open end;   a drive mechanism including a motor that is operable to drive movement of the surface of the support member and the tube relative to one another along an axis and into contact with one another;   a circuit including a voltage source and the tube; and   a control module in communication with the drive mechanism and the circuit, and configured to calibrate a relationship between the drive mechanism and a position of the tube or the surface along the axis, based on a sensed change in an electrical property of the circuit that occurs when the tube and the surface contact one another.   
     
     
         2 . The instrument of  claim 1 , wherein the drive mechanism is operable to drive movement of the surface of the support member and the tube relative to one another in three dimensions. 
     
     
         3 . The instrument of  claim 2 , wherein the drive mechanism is operable to drive movement of the surface of the support member and the tube relative to one another along each axis of a pair of orthogonal axes, and wherein the control module is configured to separately calibrate a relationship between the drive mechanism and a position of the tube or the surface along each of the orthogonal axes. 
     
     
         4 . The instrument of  claim 3 , wherein the drive mechanism includes respective motors to drive movement of the surface of the support member and the tube relative to one another along each of three orthogonal axes. 
     
     
         5 . The instrument of  claim 1 , wherein the circuit includes a resistor arranged in series with the voltage source and the tube. 
     
     
         6 . The instrument of  claim 5 , wherein the circuit branches between the resistor and the tube to form a first branch and a second branch, wherein the tube is included in the first branch, and wherein the control module is configured to sense the electrical property via the second branch. 
     
     
         7 . The instrument of  claim 6 , wherein the first branch of the circuit is open when the tube is spaced from the surface of the support member and is closed when the tube contacts the surface of the support member. 
     
     
         8 . The instrument of  claim 1 , further comprising a sample holder configured to be supported on the support member and having a well to hold fluid, wherein the control module is configured to send a drive signal to the drive mechanism that places the open end of the tube into the well. 
     
     
         9 . The instrument of  claim 8 , wherein the sample holder is configured to be mated with the support member to positively locate the sample holder. 
     
     
         10 . The instrument of  claim 8 , wherein the open end of the tube forms a port at which fluid enters the fluid-transport device, and wherein the fluid-transport device is configured to aspirate fluid from the well via the open end of the tube. 
     
     
         11 . The instrument of  claim 8 , wherein the sample holder includes an array of wells, and wherein the control module is configured to control placement of the open end of the tube into each of the wells by operation of the drive mechanism. 
     
     
         12 . The instrument of  claim 1 , wherein the fluid-transport device includes a source of positive or negative pressure operatively connected to the tube. 
     
     
         13 . An instrument having a calibration system, comprising:
 a support member including an electrically grounded, conductive surface;   a sample holder configured to be disposed on the support member and having a well;   a pipettor including an electrically conductive tube having an open end that forms a port at which fluid enters the pipettor;   a drive mechanism including a plurality of motors that are operable to drive movement of the surface of the support member and the tube relative to, and into contact with, one another along each of three orthogonal axes;   a voltage divider circuit including a voltage source, a resistor, and the tube connected in series; and   a control module in communication with the drive mechanism and the circuit and configured to separately calibrate a relationship between the drive mechanism and a position of the tube or the surface along each of the three orthogonal axes based on a change in an electrical property of the voltage divider circuit that occurs when the tube and the surface contact one another, and to control operation of the drive mechanism to place the open end of the tube into the well.   
     
     
         14 . A method of calibrating an instrument, the method comprising, in any order:
 positioning an electrically conductive tube of a fluid-transport device near a grounded, electrically conductive surface;   moving the tube and surface relative to one another along an axis with a drive mechanism until the tube and the surface come into mechanical contact with one another;   detecting when the tube and the surface come into mechanical contact by sensing an electrical property of a circuit including a voltage source and the tube; and   calibrating a relationship between the drive mechanism and a position of the tube or the surface along the axis based on the step of detecting.   
     
     
         15 . The method of  claim 14 , further comprising a step of transporting fluid through the tube. 
     
     
         16 . The method of  claim 14 , wherein the step of detecting is performed using a resistive voltage divider circuit comprising a resistor in electrical series with the tube and the voltage source, and wherein the resistance of the resistor is greater than about 1,000 Ohms. 
     
     
         17 . The method of  claim 14 , further comprising a step of stopping movement of the tube and the surface relative to one another when the mechanical contact is detected. 
     
     
         18 . The method of  claim 14 , further comprising a step of determining a difference between an actual contact point and an expected contact point of the mechanical contact, wherein the step of calibrating is based on the difference. 
     
     
         19 . The method of  claim 14 , where the axis is a first axis, the method further comprising repeating each of the steps for a second axis that is orthogonal to the first axis. 
     
     
         20 . The method of  claim 14 , wherein the step of positioning is based on nominal calibration values. 
     
     
         21 . The method of  claim 14 , further comprising steps of
 placing a sample holder on the surface;   placing an open end of the tube into a well of the sample holder by operation of the drive mechanism; and   aspirating fluid from the well into the tube.